Mobile folding stage units are used for setting up temporary staging in multi-use spaces, such as auditoriums, convention halls and meeting rooms. A typical mobile folding stage unit has a pair of platform sections pivotably mounted on a frame which are folded to parallel, upright positions for convenient storage and opened to a horizontal position on fold-out legs for staging use. The unit frame typically has roller wheels to allow the unit to be wheeled away for storage. In general, conventional units provide some mechanism for retracting the roller wheels when the platform sections are opened to the horizontal position for use.
For example, a conventional mobile folding stage unit is illustrated in FIG. 6 having a pair of stage surface members 101 supported on main support legs 102 which are braced by pivotable lower cross braces 103 and upper cross braces 104 and 105. Wheels 106 are mounted to a wheel retracting assembly pivotably mounted to the lower ends of the main support legs 102. When the stage unit is to be opened and located in a fixed position, the installer pulls a release pin (not shown) and rotates the wheels 106 to an upward position above the ends of the support legs 102 using the handles 107. The support legs also have telescoping leg sections 108 for elevating the stage surface to higher height levels. The wheel retracting mechanism for this type of stage unit assembly has the problem that manual releasing and re-locking actions are required of the installer when the unit is to be shifted between use and storage.
Another type of conventional mobile folding stage unit is illustrated in FIGS. 7A and 7B having a pair of platform members 111a, 111b pivotably supported on a lower frame 112. Wheels 113 are mounted to the ends of cross braces 114a, 114b for inwardly pivoting movement. The cross braces are pivotably mounted at one end to the frame 112 at the pivot points 115a, 115b and on the opposite end to the fold-down outer legs 116a, 116b. When the folded unit shown in FIG. 7A has been wheeled to its intended position, the platform sections 111a, 111b are opened outwardly to the horizontal position, and the follower movement of the attached cross braces 114a, 114b causes the wheels 113 to be rotated above the lower bar 112a of the frame 112, thereby retracting them out of the way. However, this type of wheel retraction mechanism requires a relatively expensive frame structure and pivot mountings for the cross braces and wheels. The pivot mountings 115a, 115b for the cross braces must be tight enough to ensure that the stage does not sway under weight, yet loose enough to allow folding of the platform sections for storage.
A further type of conventional mobile folding stage unit is illustrated in FIGS. 8A and 8B having a pair of platform members 121 pivotably supported on an upper frame 130 to which main support legs 131 are rigidly connected by cross brace 122. Linkage bars 123 are connected between the pivoting ends 121a of the platform members 121 and the pivotable holder bars 124 (at pivot points 126). The wheels 125 are mounted to plates 128 connected to the holder bars 124 for outwardly pivoting movement. When the stage unit is folded with the platform members 121 in vertical positions, the linkage bars 123 pivot the outer ends of the holder bars 124 downward so that the wheels 125 make contact with the ground below the ends 129 of the main support bars 131. As the platform members 121 are opened to the horizontal position, the downward pivoting movement of their inner ends causes the linkage bars 123 to lift the outer ends of the holder bars 124 and wheels 125 to a height above the ends 129 of the support bars 131, so that the wheels become retracted out of the way. However, this type of wheel retraction mechanism has a relatively complex and costly structure for the frame, linkage bars, and holder bars, and is rather difficult to assemble.